Electronic device manufacturers strive to produce a rich interface for users. Conventional devices utilize visual and auditory cues to provide feedback to a user. In some interface devices, kinesthetic, and/or vibrotactile feedback (such as active and resistive force feedback, vibration, texture, heat, etc.) may also be provided to the user, more generally known collectively as “haptic feedback.” Haptic feedback can provide cues that enhance and simplify the user interface.
Haptic feedback devices may rely on a friction force to output a haptic effect to a user. Materials used in such a device may wear prematurely or unevenly as a result of friction between moving elements. The coefficient of friction between moving elements in such a device may change over time as a result of this wear. The performance of a resistive haptic feedback device may be altered by the wear caused by friction forces.
The performance of a magnetic circuit may vary inversely with the square of a magnetic circuit air gap. A magnetic circuit may also suffer from the effects of residual magnetization between magnetic elements if the magnetic circuit air gap is not large enough. In a device employing a magnetic brake haptic actuator, the magnetic circuit air gap may be important to the overall performance of the device.
Thus a need exists for providing controlled friction in a haptic feedback device.